QMessageBox are not displayed if screen is off using a script

I use the attached Bash script to toggle my monitor because I am a blind user so only need the screen when a sighted person helps me.
Since PySide6, QMessageBox are not displayed if I used this script to switch my monitor off. When it is on, I have no issue at all.
When parent is set to a QMainWindow or QDialog, interface is not blocked, until the application is closed. When set to None the script freezes directly, even pressing Ctrl+c does not end it.
it does not occur E.G. with QInputDialog